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The Short Answer
- Perforation gauge is measured by the number of holes per 2 centimeters.
- Different perforations on the same stamp can create major varieties.
- Watermarks are hidden designs embedded in stamp paper.
- AI can measure perforation and assist watermark detection from images.
Perforation Gauge
Perforation gauge is the number of perforation holes per 2 centimeters. Common gauges include 11, 12, and 13. A small difference can separate a common stamp from a rare variety.Coil and Imperforate Varieties
Coil stamps are produced in rolls and have straight edges on two sides. Imperforate stamps have no perforations. Both can be rare depending on the issue.Watermark Types
Watermarks include letters, symbols, and designs embedded in the paper. Common watermarks include the Crown CC, Multiple Crown CA, and US double-line USPS watermarks.AI Detection
AI can measure perforation spacing from high-resolution photos and detect watermark patterns when the stamp is backlit. This helps collectors quickly identify potential varieties.Frequently Asked Questions
What is a perforation gauge?
Perforation gauge is the number of holes per 2 centimeters along the stamp edge. It is used to identify varieties.
Why are imperforate stamps rare?
Most stamps are perforated. Imperforate stamps are usually errors or special printings, making them scarce.
What is the most common watermark on US stamps?
The double-line USPS watermark is common on many classic US issues.
Can AI replace a perforation gauge?
AI can measure perforation from photos, but physical measurement tools remain the gold standard for valuable varieties.
Sources & Further Reading
PreGradeCards Research Team
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The PreGradeCards Research Team combines machine-learning engineers, grading analysts, and collector-education specialists to produce accurate, data-driven guides on AI card grading, professional grading standards, and collecting strategy.
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